Process of protecting ferrous metals



Patented Oct. 24, 1933 PROCESS OF PROTECTING FERROUS METALS Stanley 0. Moore and Frank E. Bowker, Toledo, Ohio, assignors to The Dura Company, Toledo, Ohio, a corporation of Ohio No Drawing. Application March 2, 1931 Serial No. 519,680

17 Claims. (01. 204-13) The invention relatesto a novel finish for articles of manufacture which renders them more suitable to various requ rements of use. While the invention may be applied to a wide diversity 5 of articles, its particular utility is in connection with metal articles having a ferrous base.

The main object of the invention is to procure a finish having the following properties:

1. Extremely resistant to corrosion (rusting). 2. Resistant to acid and chemical vapors from foodproducts. I l

3. Surface hardness. 4. Flexibility of coating.

5. Good color either polished orunpolished.

' 6. Ability to maintain appearance and to be readily cleaned. I I

'7. Adaptable to commercial methods of production resulting in low cost factor.

Another' object of the invention is to improve upon the relation of the metals in a multiple coat finish in order to obtain improved properties in thefinish.

A further object is to provide improved processes forapplying the various coatings whereby 0 the resultant product has improved characteristics. v

Another object is to provide such improvement in the processes for obtaining successive coatings that the cost of producing a finish of given characteristics is greatly reduced.

These and other objects may be attained by following the practices hereinafter more fully described.

The invention in one of its broader aspects consists of a multiple coating finish in which the various layers of metal or alloy are arranged in a definite relationship and have certain physical and chemical characteristics which cooperate with each other to attain new and improved properties in the finish as a whole. For example, the invention contemplates a finish in which a ferrous metal object is first coated with cadmium or some other electropositive metal which protects the ferrous metal by preferential oxidation. The object is then treated in such a way as to provide a covering of metal or alloy which will completely protect the cadmium from corrosion producing elements and at the same time provide the outer surface with properties for resisting wear, abrasion, tarnishing, chipping, etc.

We have discovered that a very dense electrodeposition of nickel intermediate the cadmium aforesaid and a final coating of chromium will, if properly applied according to .our invention, give the desired protection to the cadmium. Thus a finish ofchromium on nickel on cadmium on a ferrous base comes within the purview of our invention if the nickel is of suflicient thickness and density to form a complete impervious covering for the cadmium.

Our invention also contemplates a finish superior to the above in corrosion-resisting properties where the intermediate layer of nickel is modified to obtain a more impervious covering with less total thickness of deposit. For example, the nickel layer may be replaced with the combination layer nickel, copper, nickel so that the complete finish is chromium on nickel on copper on nickel on cadmium on a ferrous base. This last mentioned finish has been found to have remark'ablecorrosion-resisting properties and tests have revealed no sign of corrosion after many hundreds of hours in the salt spray test. The relationship of the metals themselves in this combination coating is one of the underlying reasons for the advantageous properties of the finish as a whole Another important feature of our invention is the relationship of the thicknesses and densities of the various layers. To obtain flexibility and freedom from chipping in the final finish all of the layers must be strongly adherent and the total thickness of the finish must not be too great. Thus our invention contemplates a finish in which some of the layers are relatively thin and others are relatively thick, the relationship being such as to give themaximum protection against corrosion with the maximum durability and the cheapest cost of production on a large commercial scale.

By preference therefore the first coating of nickel on the cadmium is relatively thin and the copper coat on the first nickel is also thin while the second nickel coat on the copper is relatively thick and dense. This relationship while not essential to the invention in its broader aspects is nevertheless an important feature of our preferred finish.

We will now describe in detail one process for obtaining the' finish chromium on nickel on copper on nickel on cadmium on a ferrous base. This process is adaptable for use on a continuous plating machine.

The ferrous base is first cleaned of rust and scale. This may be done by ordinary plating room methods or it may be done by electrolytic cleaning. One method is to subject the articles as cathodes in a soap-cleaning solution. Following the cleaning, the articles are dipped in a clean water rinse and then subjected as cathodes in a suitable pickling solution, preferably using hydrochloric acid. The objects are then thoroughly rinsed in clean water and are ready for receiving the first metallic coating. It is to be understood that further cleaning steps may be employed if it is found necessary or desirable in order to obtain a thoroughly clean surface for the initial electrodeposition. The object is then immersed in a cadmium plating bath and a layer of cadmium is built up on the object to the desired thickness.

While our invention is not necessarily limited to any specific cadmium plating process, the following solution has been found to give excellent results:

Ozs. per gal.

Cadmium oxide (CdO) Sodium cyanide (NaCN) Sodium sulphate (Na SO +10H O) Nickel sulphate (Nis0.,+eH20) 0.2

The current density is preferably maintained between 10 and 20 'amperes per square foot and the anodes are commercially pure cadmium.

After securing the required thickness of the cadmium deposit the object is thoroughly washed and then placed immediately in a nickel plating bath. In order to obtain a satisfactory electrodeposition of nickel on the cadmium plate a special nickel plating process must be used. A desirable electrolyte may be prepared as follows:

Ozs. per gal. Nickel sulphate (NiSO i SE20) 10-24 Sodium sulphate anhydrous (Na SO 16-24 Sodium chloride (NaCl) 2 Boric acid (HQBOS) 2 The current density is preferably maintained between 10 to 30 amperes per square foot and nickel anodes are used. It is important that the hydrogen ion concentration of the electrolyte be maintained within definite limits in order to satisfactorily plate the nickel over the previous cadmium coating and we have found that the best range for the pH value is 5.6 to 6.0. These values are not necessarily absolute and under certain The current density is preferably maintained at 15 to 25 amperes per square foot and a copper anode is used. The copper plating is continued until the previous nickel plating is thoroughly covered with copper and the article is then removed, thoroughly washed and again submitted to a nickel plating bath. This second nickel plating solution is preferably a different composition than that used for plating over the cadmium. The solution is of such a character that high current densities may be used in order that a dense deposition may be obtained. It is also desirable to provide such a process as will permit a heavy coating to be obtained in a" relatively short time interval so that a continuous dense impervious coating of nickel will be deposited over the entire article and serve as a complete protection for the underlying cadmium layer,

The solution recommended for this process has the following composition:

Ozs. per gal. Nickel sulphate 30-42 Nickel chloride 4 Boric acid 4 The current density may range up to 100 amperes per square foot, although a desirable range for continuous production may preferably be approximately 50 amperes per square foot. The pH value is mantained between 1.0 and 7.0 and nickel anodes are used. The pH value bears a relation to the current density and in general the higher current densities require a lower pH value in order to obtain satisfactory results. Better deposition of nckel for the purposes of this invention is obtained when the temperature of the bath is maintained above normal room temperature, the range being ordinarily from 70 F. to 180 F. For practical results in a continuous plat- :ng bath we have found that satisfactory results are obtained with a current density of 50 amperes per square foot, a pH value of 2.5 and a temperature of 110 F. to 125 F.

- As heretofore stated it is preferable that the object be heavily coated with nickel in the above mentioned bath, although the exact thickness of the coating depends upon the relation thereof to the other coatings in the finish.

After completing the nickel deposit the article is thoroughly washed and subjected to a chromium plating solution. A satisfactory solution for carrying out the chromium plating has the follow ng composition:

Ozs. per gal. Chromic acid (CrOa) 35 Zinc sulphate (Zn SO4+6H2O) .445

The anodes used for the chromium plating bath are lead and the current density may range from to 200 amperes per square foot. The temperature of the bath is preferably maintained from 80 F. to 140 F. The thickness of the chrom um layer may be varied depending upon the use to which the object is to be put but for many articles of manufacture a relatively thin layer of chromium is sufficient.

The various steps of the process as above set forth utilize plating solutions which will permit the electrodeposition of successive layers of different metals without interference of one metal on the other. Furthermore, a good bond may be obtained between the various metals such that the finish will not peel or chip off under ordinary conditions.

As heretofore mentioned, the above process is adapted for a substantially continuous operation if suitable automatic machinery is provided for ths purpose.

The thicknesses of the various layers depend upon the conditions of each individual plating operation and with any given conditions of electrolytic composition and current density, the

thickness depends upon the time allotted for each nickel or alloys of nickel and cobalt. It is, how- Ferrocs base Inch Cadmium .0001 Nick .00005 Copper .00005 Nickel .0002 Chromium .00005 process which lends itself to very speedy electrodeposition. Thus by means oi the particular process as hereinbeiore set forth, we are enabled to obtain an adequate protective covering for the cadmium with a process adapted for quantity production.

While we have heretofore discussed'the preferred composition,

Ferrous tase-od-m-cu-m-cr our invention in its broader aspects is generic to 'many other combinations, some of which will now be given by way of example. In place of cadmium any other electronegative metal may be used in contact with the ferrous base. Thus the invention includes zinc in place of cadmium giving the composition:

Ferrous base-Zn-Ni-Cu-Ni-Cr As a substitute for the intermediate layers between the electropositive metal and the final metal, a series of alternate coats of nickel and copper may be used, giving for example the composition:

Ferrous base-Cd-Ni- -Cu-Iii-CuNi-Cr In such finish either the second or the third nickel coating is preferably made of the greatest thickness.

One of the objects of using a multiple coating such as nickel-copper-nickel intermediate the cadmium and the chromium is to insure freedom from pin holes in the cadmium-protecting layer.

The series of layers eliminates some of the pin hole spots which might be present if a single nickel coating of merely the thickness of the combined nickel, copper, nickel coating were used. The same object, however, might also be obtained with metals other than copper intermediate the two nickel layers. Other ductile metals might be used and'still retain resiliency and freedom from chipping but in general it is desirable that such metal be substituted for the copper which is capable of being deposited from a cyanide solution. For example considering the physical and chemical properties alone, a flash coating of silver intermediate the nickel layers would be equivalent to the copper since the silver is capable of deposition from a'cyanide solution. Other metals which might be used intermediate the nickel layers are cadmium or zinc, each of which may be deposited from a cyanide solution. However, it will be clearly apparent that from a practical standpoint a. copper layer intermediate the nickel deposits is by far superior.

It also comes within the purview of the invention to substitute other metals or alloys for the nickel layers. Cobalt may be used in place of ever, necessary that at least one layer of the nickel or nickel substitute be relatively thick and of such density as to maintain an impervious layer intermediate the first coating of cadmium and the final coating of chromium.

What we claim as our invention is:

1. An article of manufacture comprising a for rous base, a layer of a metal electronegative to iron on said base, an outer coating of chromium and a relatively thick continuous layer of nickel intermediate said electronegative metal and said chromium.

2. An article of manufacture comprising a ferrous base, a layer of metal electronegative to'ircn on said base, an outer coating of chromium and a plurality of layers of diflerent metals inter-= mediate said electronegative layer and said chro mium. r

3. An article of manufacture comprising a ier rous base, a layer of a metal electronegative to iron on said base, an outer layer of chromium and a plurality of layers intermediate said electronegative metal and said chromium including nickel layers directly in contact with both said 1069 electronegative metal and said chromium.

4. An article of manufacture comprising a terrous base, a layer of a metal electronegative to iron on said base, an .outer layer of chromium and alternate layers of nickel and copper intermediate said electronegative metal and said chro- 5. An article of manufacture comprising a i'errous base, a metal electronegative to iron directly rous base, a layer of a metal electronegative to iron on said base, a layer of nickel on said electronegativ'e metal, a layer of copper on said nickel, a layer of nickel on said copper and an outer coating of chromium 8. An article of manufacture comprising a ferrous base, a layer of a metal electronegative to iron directly on said base, a layer of nickel dlrectly on said electronegative metal, a layer of copper directly on said nickel, a layer of nickel directly on said copper and a layer of chromium directly on said nickel.

9. An article of manufacture comprising a ferrous base, a layer of a metal electronegative to iron on said base, a flash coating -of nickel on said electronegative metal, a flash coating of a metal capable of being deposited from a cyanide solution on said nickeland a layer of nickel at least one-half thousandthof an inch thick on said last mentioned metal.

10. An article of manufacture comprising a ferrous base, a layer of a metal electronegative to iron on said base, a flash coating of nickel on said electronegative metal, a flash coating of a metal capable of being deposited from a cyanide solution on said nickel, a layer of nickel at least one-half thousandth of an inch thick on saidw last mentioned metal, and an outer coating of chromium.

11. An article of manufacture comprising a ferrous base, a layer of metal electronegative to iron on said base, a flash coating of nickel on said electronegative metal, a flash coating of copper on said nickel and a layer of nickel at least one thousandth of an inch thick on said copper.

12. An article of manufacture comprising a ferrous base, a layer of metal electronegative to iron on said base, a flash coating of nickel on said electronegative metal, a flash coating of copper on said nickel, a layer of nickel at least one thousandth of an inch thick on said copper and an outer coating of chromium.

13. An article of manufacture comprising a ferrous metal base, a layer of metal electronegative to iron on said base, a flash coating of a metal capable of being deposited from a cyanide solution and a layer of nickel at least one thousandth of an inch thick.

" 14. An article of manufacture comprising a ferrous metal base, a layer of metal electronegative to iron on said base, a flash coating of a metal capable of being deposited from a cyanide solution, a layer of nickel at least one thousandth of an inch thick and an outer layer of chromium.

15. An article of manufacture comprising a ferrous base, a layer of metal electronegative to iron on said base and a relatively thick continuous coating of a dense fine grained metal such as nickel, cobalt or tin and an outer coating of chromium.

16. An article of manufacture comprising a metal base and successive layers of cadmium, nickel, copper, nickel and chromium on said base.

17. An article of manufacture comprising a ferrous base and successive layers of cadmium, nickel, copper, nickel and chromium on said base.

STANLEY C. MOORE. FRANK E. BOWKER. 

